1. Field of the Invention
The present disclosure relates generally to quadrupole mass filters used in mass spectrometers.
2. Description of the Related Art
Quadrupole mass spectrometers require a large RF voltage with a typical amplitude of several kilovolts. This voltage must be produced and connected to the quadrupole mass filter that resides inside a vacuum chamber. To efficiently achieve the required voltage, large coils or transformers are utilized in the RF drive circuit and are resonated with the capacitance of the quadrupole mass filter. Typically the RF drive circuit is designed around a separate box with RF coils or a transformer inside. This assembly is at atmospheric pressure, not under vacuum. The RF voltage generated by the inductors in the box is then delivered to the quadrupole mass filter in the vacuum chamber using a vacuum feedthrough and involves various wires, cables and flex boards both inside and outside of the vacuum chamber. A conventional arrangement is shown in FIG. 1, in which an RF drive circuit 102 uses a pair of RF coils 104 to generate the large voltages required. This voltage is delivered from RF board 106 using freestanding wires 108 (only two are shown) that pass by way of vacuum feedthrough 110 into the vacuum chamber 112. The wires 108 connect to a flexible circuit board (flex board) 114 in the vacuum environment, often by way of additional intervening circuit boards and freestanding wires (not shown). From flex board 114, RF energy is then distributed to the various rods 116 of the quadrupole mass filter.
The resonant frequency of the circuit is affected by the variability of stray capacitance in all of the connection components, and is specific to the particular configuration of these flexible components as last established after assembly and after any subsequent adjustment and handling. Thus, because the flexibility of the components is attended by variability in their capacitance and/or inductance signatures, the circuit must be tuned into resonance using a tuning mechanism 118 that will re-adjust either the capacitance or inductance in the circuit. This tuning, which is arduous and time consuming, must be performed following each intended or unintended change in configuration of the flexible connection components that inevitably attends every handling, for example after circuit board removal for inspection or replacement.